1. Field of the Invention
The present invention relates to communication satellites. More particularly, the present invention relates to communication satellites that operate in the C-band and the Ku-band.
2. Discussion of the Related Art
Conventionally, communication satellites were confined to telephone communications. However, many forms of communication are now being relayed by geo-synchronous satellites including, but not limited to, voice, data, video, television, and radio. Several major industries are heavily dependent upon reliable satellite communications service being continuously available.
FIG. 1 is an illustration of a satellite communications network in which two satellites provide redundancy for communications. Satellites 10 and 20 communicate with ground stations 30 located within a region of Earth 40 using a uniform distribution methodology. This uniform distribution methodology allows for communications to an entire region of Earth 40, such as, but not limited to, North America. If one of the satellites 10 or 20 should ever fail, then the other satellite may take over its communications function. However, this redundancy is expensive to implement since two satellites must be used in case one fails. Further, should demand increase in one location, it may not be possible to reconfigure the satellites in orbit to handle the additional load from the increased traffic seen in one area.
One mechanism utilized to overcome the foregoing problems of redundancy and capacity has been to utilize multiple feeds to form multiple spot beams to target specific locations on Earth 40. Conventionally, only a relatively small number of feeds could be placed within a single antenna due to the large feed horn size. However, as illustrated in U.S. Pat. Nos. 6,211,835, 6,215,452 and 6,236,375, the subject matter of which are hereby incorporated by reference in their entirety, it is now possible to have a large number of spot beams in which each spot beam individually targets specific locations on Earth 40 using hemispherical earth coverage antennas.
FIG. 2 is an example illustration of spot beams positioned over predefined Earth locations utilizing hemispherical earth coverage antennas. A satellite positions its spot beams 50 to cover South America and the east coast of the United States from its location at 45 degrees west longitude. More than one spot beam may be directed at any given location within the range of the satellite. Further, the positioning of the spot beams is dependent upon the physical alignment of the feeds in the antenna of the satellite and the longitude at which the satellite is positioned in geo-synchronous orbit as detailed in U.S. Pat. Nos. 6,211,835; 6,215,452; and 6,236,375. The spot beams may be directed towards those areas where demand is highest and profitability maximized. Therefore, the positioning of feeds to generate spot beams may be critical in determining the profitability and redundancy of a satellite communications network.